1. Field of the Invention
This invention relates to an electrophotographic endless belt such as an intermediate transfer belt or a transfer material transporting belt, and also relates to a process for producing the electrophotographic endless belt, and an electrophotographic apparatus having the electrophotographic endless belt.
2. Related Background Art
Besides rigid-body drum-shaped members, flexible endless-belt-shaped members (electrophotographic endless belts or electrophotographic seamless belts) are conventionally used in transfer material transporting members, intermediate transfer members and so forth used in electrophotographic apparatus such as copying machines and laser beam printers.
In recent years, color (such as full-color) electrophotographic apparatus have been put forward into practical use, and there is an increasing demand for electrophotographic endless belts as well, such as transfer material transporting belts and intermediate transfer belts.
In recent years, as an electrophotographic endless belt, an endless belt having a layer (resin layer) formed of a resin composition containing a resin is in wide use.
As the resin used in this resin composition, for example, polycarbonate is disclosed in Japanese Patent Applications Laid-open No. H03-089357 and No. H05-345368, an ethylene-tetrafluoroethylene copolymer (ETFE) is disclosed in Japanese Patent Application Laid-open No. H08-025232, and a polymer blend of polyalkylene terephthalate and polycarbonate is disclosed in Japanese Patent No. 2,845,059.
However, the use of these resins in the electrophotographic endless belts involves the following problems.
For example, the polycarbonate has a disadvantage that it has not so high resistance to cracking and hence, where an endless belt making use of this resin is repeatedly used, it tends to cause cracking, resulting in a short lifetime.
The ethylene-tetrafluoroethylene copolymer also has a disadvantage that it tends to cause creeping and hence, where an endless belt making use of this resin is repeatedly used, the endless belt may come to stretch, resulting in a short lifetime. As a method for making the level of creeping smaller, a method is available in which the endless belt is made in a large thickness. However, making the endless belt in a large thickness results in a low resistance to cracking. A method is also available in which a mechanism for changing the tension to be applied to the endless belt in accordance with the length of the endless belt is added to an endless-belt stretch-over mechanism provided in the main body of an electrophotographic apparatus, to keep the endless belt from undergoing difficulties due to creeping. In this case, however, component parts are required in a larger number, and this necessitates the main body of the electrophotographic apparatus to be larger and causes a rise in cost.
The polymer blend of polyalkylene terephthalate and polycarbonate promises some higher resistance to cracking than the polycarbonate. However, under actual circumstances, it can not completely sufficiently meet the demand for higher image quality and higher running (extensive-operation) performance in recent years.
As a method for solving these problems, a method is available in which a polyamide, having a high toughness among engineering plastics, is used in the electrophotographic endless belt (see, e.g., Japanese Patent Applications Laid-open No. H11-352796 and No. 2001-350347.
However, the polyamide has a large rate of change in melt viscosity with respect to temperature, and hence extrusion stability may lower also by the deflection of extrusion conditions, resulting in a large thickness non-uniformity. If such an electrophotographic endless belt having a large thickness non-uniformity is used as an endless belt-shaped transfer member such as the transfer material transporting belt or the intermediate transfer belt, the belt may have a poor transfer performance. Stated specifically, transfer non-uniformity or blank areas caused by poor transfer may occur on reproduced images.